Preparation Of Chelating Fibers Containing Amine Group And Their Adsorption Behavior For Heavy Metal Ions

Chelating fiber is a kind of ion exchange fiber. It possesses not only all the advantages of ion exchange fiber, but also some advantages that other ion exchange fibers do not have, such as high selectivity and adsorption capacity for metal ions. Therefore, chelating fiber has been widely used in the treatment of nuclear and industrial wastewater, purification of toxic gas, enrichment of precious metals, biomedical engineering, electronic chemicals, purification and recycling.This paper has synthesized a series of chelating fibers with excellent mechanical properties as well as good adsorption performance by grafting some monomers (glycidyl methacrylate, acrylonitrile, acrylic acid) having active functional groups onto the matrix fibers (polypropylene, PP fibers), followed by aminating with diethylenetriamine to introduce amine group that possess strong chelating ability for heavy metal ions. Effects of the grafting conditions such as monomer concentration, irradiation method and dose, reaction temperature, reaction time, solvents and catalyst dose on the grafting degree were investigated. The chemical structure, thermal stability and mechanical properties of the chelating fibers were characterized with Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and monofilament tensile test. Adsorption performances of the chelating fibers were investigated. 1. Chelating fiber PP-GMA-DETA was prepared by solution grafting copolymerization of glycidyl methacrylate(GMA) onto polypropylene fiber through pre-irradiation and co-irradiation, followed by aminating with chelating molecule diethylenetriamine. The grafting degree of PP grafted GMA can reach 240% under the optimal grafting conditions (reaction time 3h, temperature 100℃, 50% monomer concentration, tetrahydrofuran as solvent).The chelating fiber has a very good adsorption performance for Hg2+. The adsorption capacity in aqueous solution is 785.28mg/g as the initial concentration of mercury is 1000mg?L-1. The chelating adsorption capacity for Hg2+ will not be considerably affected by coexistence of copper ions within the concentration of Cu2+ is 1-10 times concentration of Hg2+2. An aminated chelating fiber PP-AN-DETA was prepared by irradiation grafting copolymerization of acrylonitrile(AN) onto polypropylene fiber, followed by aminating with diethylenetriamine, taking advantage of the reactivity of cyano group. Effects of grafting conditions including temperature, reaction time, bath ratio and dosage of catalyst on the grafting degree of PP grafted AN have been studied, in which reaction temperature and reaction time have the greatest impacts on grafting degree. Under the optimal grafting conditions, the grafting degree can reach 282%. Chelating fiber PP-AN-DETA presents good adsorption performance for mercury ions. The equilibrium adsorption amount can reach 657.9mg/g. The adsorption behavior of PP-AN-DETA is in good accordance with Langmuir isotherm model and Freundlich isotherm model. By comparing the theoretical adsorption capacity based on the content of N element and the experimental adsorption capacity calculated from the Langmuir isotherms, it may be speculated that the chelating mechanism is mainly through chelating interaction between nitrogen-containing functional groups and mercury ions.3. Chelating fiber PP-AA-DETA having amine and carboxyl functional group was synthesized by irradiation grafting copolymerization of acrylic acid monomer containing hydrophilic active functional group onto polypropylene fiber, sequently aminating with diethylenetriamine. Surface tension test results show that the process of grafting acrylic acid and amine preparation improve the hydrophilic properties of the fibers. Under the optimized grafting conditions, the grafting degree can be as high as 340%. Adsorption capacity of the chelating fiber for mercury, which can reach as high as 1038.8 mg/g, is proportional to the grafting degree and the content of amine groups. When comparing theoretical adsorption capacity calculated by two amine groups chelating with one mercury ion and the maxium adsorption capacity, it can be found that the adsorption mechanism is the synergic adsorption of chelating adsorption and the ion exchange adsorption of carboxyl groups and mercury ions. The adsorption capacity of PP-AA-DETA for mercury increases with the increasing adsorption temperature, which indicates that the adsorption is an endothermic process, and the adsorption enthalpyΔH o is -11.67kJ/mol.4. By grafting copolymerization of monomers (AN, GMA) onto agricultural by-products bagasse, then aminating with diethylenetriamine, an amine modified bagasse fiber was prepared. The chelating fibers are effective with the removal of mercury in a wide range and possess higher adsorption capacity when pH over 3, the adsorption amount can reach 1185.0mg/g-1 when C0 is 1000mg/L-1. With 3M HCl +0.5% CS (NH2) 2 as the eluting agent, amine modified bagasse can still reach 96% of removal efficiency and 85% of recovery efficiency after four consecutive adsorption-desorption cycle, and the morphology of the fiber can be maintained.5. The chelating fibers prepared by the processes above can maintain good thermal stability and mechanical properties. They are effective for mercury removal in a wide pH range and keep strong adsorption force for mercury ions. It is demonstrated that not only the adsorption capacity of the chelating fibers is quite strong, but also they can thoroughly remove mercury in low concentration of wastewater. When the low concentration of mercury-containing wastewater was treated by such chelating fibers, the residual mercury concentration in the solution can be reduced to 1μg/L. These results show that the chelating fibers have a good prospect of application in wastewater treatment and drinking water purification.